Electronic film development is a process in which conventional silver halide film is electronically scanned during the actual development process, rather than waiting, as in the common art, until development is finished. Electronic film development is taught in U.S. Pat. No. 5,519,510 issued to the present inventor.
With electronic film development it is possible to build a history of the emerging image through different phases of development. Early in development, highlights reveal the greatest clarity. Conventional development would proceed past this point into total darkness, but by capturing the image at this time, highlight details that would normally be lost are saved. Conversely, conventional development would end development at the optimum compromise point. But by developing past that time and continuing to capture the image during continued development, image details that would normally be lost can be coaxed from the shadows.
Thus, one key to electronic film development is the ability to capture images of the same piece of film at different development times and to later merge these images into one image with more detail than in conventional development. This merging is called xe2x80x9cstitchingxe2x80x9d. In the prior art, stitching was performed by effectively cutting out and aligning parts of the different development time images, and pasting those image fragments back together.
This system is capable of coping with variations or jumps in sample times that would confuse the prior art method of stitching. For example, if all the samples were made 30 seconds later, but all the densities were proportionately higher, the same continuous curve would of course be described without special corrections required to make individually captured image densities coalign.
Additional background art is described in U.S. Pat. No. 5,465,155 developed by Al Edgar. This known process extends electronic film development to tricolor image capture. In duplex film scanning, a conventional multilayer color film is scanned during development in three ways: by reflected light from the back, by reflected light from the front, and by transmitted light from either the front or back. Each of these three ways of scanning xe2x80x9csees,xe2x80x9d to varying degrees, the front, middle, and back layers of the multilayer film. By mathematically differencing the images seen in these three ways, all colors can be distinguished and, through color mapping techniques, can be assigned to the correct colors.
FIG. 1 presents a basic apparatus for electronic film development. A filmstrip 102 is placed under development by immersing the entire film in a transparent developing tank (not shown for clarity). During development, an infrared lamp 104 is switched on to illuminate a developing image 106 on the film. Light passing through the film 102 containing the image 106 is focused by lens 108 onto an area sensor array 110. At the same time, light reflected from the front of the film 102 containing the image 106 is focused by lens 112 onto an area sensor array 114. After the back transmission and front reflection images have been received by the sensor arrays 110 and 114 and stored in a computer memory, the lamp 104 is extinguished and the infrared lamp 120 is activated. With lamp 120 on, the sensor array 114 receives a front transmission image, and the sensor array 110 receives a back reflection image of the light from the film 102 containing the image 106. In the course of electronic film development, this process is repeated any number of times to receive multiple images made during development.
The problem with the apparatus of FIG. 1 is that only one frame can be developed at a time. The method also requires very precise placement of developer application to transition in the thin space between frames. Further, the method requires precise alignment of frames on a film before development is started. If a mistake is made in frame alignment, which is easy to do before any image has begun to develop, a seam will appear within a frame, ruining the image exposed in that frame. This hit or miss development is unacceptable for general use.
FIG. 2 presents a prior art refinement of an electronic film development apparatus. In FIG. 2, a filmstrip 202 is moved continuously to the right without requiring foreknowledge of frame boundaries. Developer is applied at station 204. At some time after application of developer, the film 202 will be positioned under line 206. At this line 206 the film 202 is scanned by two linear scan arrays: a front array 210 receives light imaged through lens 212, and a back array 214 receives light imaged through lens 216. In conjunction with front lamp 220 and back lamp 222, the front refection, back reflection, and transmission images can be received as described in FIG. 1.
In the apparatus of FIG. 2, sensor arrays 210 and 214 will always receive images of the film 202 at a specific development time fixed by the time of transport between the developer application station 204 and the line being scanned 206. A second scanning station viewing line 230, and a third scanning station viewing line 240 capture two additional images at two additional distinct times. Combined, the three scanning stations provide three views of the image in the film at three points in time.
Because of the ability to continuously move the film 202, the apparatus of FIG. 2 solved the problem of knowing frame boundaries before development. In fact, the entire film is developed seamlessly, with the assumption that further software can parse the continuous film image into separate frames.
The prior art apparatus of FIG. 2 has some serious disadvantages that severely limited the commercialization of electronic film development. The three scanning stations of FIG. 2 would cost on the order of three times that of the one scanning station of FIG. 1. Further, as explained above, an improved image would be obtained by scanning the image many more times than three. Although the apparatus of FIG. 2 could contemplate additional scanning stations, the cost would grow proportionately. Further, the line scanners of FIG. 2 require much more light than the area scanner of FIG. 1.
Another serious flaw in the apparatus of FIG. 2 is the problem in later aligning the images made at the different scanning stations. The image made along line 230 is scanned at a different development time from the image made along line 206, and therefore contains different image details. Because of the differences in these images, registration of these images in software was difficult and often done improperly since prior art software had difficulties aligning images with different sets of details. In response to the inability of software to align the images, the apparatus of FIG. 2 relied on expensive, precision mechanics for alignment, further increasing the cost. Electronic film development promised a universal film that could be used in conventional cameras and yet give unprecedented image detail as well as give a widened sensitivity range that would embrace the natural light of life without reliance on harsh electronic flash. The further promise of electronic film development was for a small development apparatus, with no plumbing, that could fit beside a desktop computer in businesses, schools, and homes to accelerate the image literacy revolution. The problems described above seriously compromised these dreams by making an electronic film development apparatus too expensive for families and schools to afford.
A primary object of this invention is to provide a simplified method of electronic film development.
A corollary object is to perform seamless scanning during film development with a single area scan station.
Another corollary object is to perform an arbitrary number of scans per film area with seamless coverage.
A further object is to perform seamless scanning at multiple times during development with a single linear array scanner.
Another object is to provide improved registration accuracy of the various scans made during the course of electronic film development.
A further object is to provide a nondiverging registration in electronic film development. Another object is to reduce computational time in registering the various scans made during the course of electronic film development.
These and other objects are accomplished in accordance with the teachings of this invention by scanning film in sequential areas that have multiple levels of overlap. The areas can be scanned by an area array or by a linear array rapidly moving so as to scan an area. The single scan area is iteratively moved with many levels of overlap to reduce the number of stations required by the prior art, thereby simplifying and lowering cost. The overlapping areas, in conjunction with other features of the present invention, prevent the seams created by the prior art method that used a single scanning station.
The scanned areas are accumulated in a film array representing the film. Each new area scanned is registered with the image already laid in the film array. This is made possible because the multiple levels of overlap insure that most of each new scan covers a part of the film previously scanned. In addition, the leading edge ahead of previous scans defines a region in which the registered new image can be warped to steer the growing image and prevent it from diverging out of the film array.
Registration is performed by first estimating, from previous scans, how the film looks at the time of a new scan, and then registering this new scan to this extrapolated estimate for increased accuracy. Once registered, the density from the new scan is accumulated in the film array as a set of parameter summations for later parametric regression of the density versus time curve for each pixel. Accumulation is weighted in a sparse fashion across the elements of the film array.
Front reflection, front transmission, back reflection, and back transmission scans are made at each time. The front and back transmissions are registered to each other, then the merged result is accumulated in a single transmission film array. The front and back reflection scans are assumed to be in perfect register with the front and back transmission scans, respectively, and therefore the registration data for the transmission scans also applies to the respective reflection scans, saving computation time.